1. Field of the Invention
The present invention relates to an analysis cell for the analysis, at very high pressure and high temperature, of samples of fluids and a detection and measuring method using said cell to determine the conditions for the formation of solid particles and, if applicable, to measure the quantity of solid matter present in said samples.
2. Description of the Related Art
A high pressure and high temperature analysis cell is in particular applicable in the analysis of the thermodynamic and physicochemical properties of hydrocarbons.
These cells are used in the laboratory to perform tests and measurements making it possible to determine the composition of the crude oil taken from a prospecting site before the industrial and commercial exploitation thereof.
These measurements are more particularly intended to determine, precisely and sometimes directly on the site of the explored deposit, any presence of solid matter and the quantity thereof in the crude oil as well as the thermodynamic behavior of that matter during so-called “PVT” tests, i.e., pressure, volume and temperature.
The search for means for determining and predicting the thermodynamic conditions that may lead to the generation of solid particles in oil fluids during exploitation thereof has become very important in the field of oil exploration.
The formation of solid particles refers to the phenomena of asphaltene flocculation or precipitation, and the formation of paraffin (wax) or hydrate crystals.
In fact, at high pressure in the deposits, the asphaltenes are dissolved in the crude oil, which is therefore in a monophasic form.
However, during the extraction of the oil by drilling, the pressure decreases while rising toward the surface and the pressure/temperature pair assumes a first critical value called AOP (Asphaltene Onset Precipitation), which corresponds to the precipitation of asphaltenes. There is also a second critical value called WAT (Wax Appearance Temperature), at which wax crystals are likely to appear. For each sample, it is possible to predict the measurement of the bubble point, which corresponds, for a given temperature, to the state change pressure of the fluid (liquid-gas).
Thus, once equilibrium is broken, through temperature or pressure variations or through a simple change in the chemical composition, a solid phase forms that may cause plugging or accidental dirtying of the conduits for the drilling and/or pipelines, which is extremely detrimental to the exploitation of the well.
It is therefore necessary to provide, from samples taken from the bottom of the well (called “bottom hole samples”), the later behavior of its asphaltene/wax/hydrate components so as to prevent them from having a negative impact during all steps of the production, transport, and refining of hydrocarbons and so as to adapt the facilities and equipment dedicated thereto.
This need is further increased for so-called “new oils,” which are primarily bituminous shales and deep oils extracted from “offshore” wells.
These heavy hydrocarbons and certain light oils are more problematic to exploit and transport, since the risk of the appearance of deposits of solid particles, during the rise in the wells and in the transport conduits due to significant pressure and temperature changes, is significantly greater than for traditional hydrocarbons.
The anticipation and/or neutralization of the risk of solid deposits is therefore a new challenge for the oil industry, which is seeking, for logistical and therefore economic reasons, guarantees with respect to the fluidity of the oil during all steps of the exploitation.
Consequently, the analysis of hydrocarbon samples, before the industrial exploitation of the deposit or in the context of the design of recovery techniques (Enhanced Oil Recovery), is henceforth undeniable. This consists of simulating and/or reproducing the thermodynamic conditions to which the hydrocarbons will be subjected during their extraction so as to assess, as a function of their composition, the risks related to the potential appearance of solid phases.
The analysis methods commonly used for biphasic fluids are based on measuring optical properties and, in particular, the diffraction and/or absorption by the solid particles within the analyzed fluid.
For petroleum fluids, the measurements are generally done either using a microscope or by lighting the sample using a laser beam in the infrared wavelengths and measuring the optical power transmitted and/or absorbed through said sample.
The absorption factor (absorbed light) or, conversely, the transmission factor (transmitted light) varies as a function both of the density of the fluid (related to the pressure and temperature conditions) and the presence (optionally also the quantity) of solid particles (asphaltenes, for example).
Regarding the equipment, the known analysis cells generally comprise a cylinder in which an axially translatable piston is mounted that defines, with the end walls of the cylinder, a compression chamber in which the sample is subjected to a very high pressure while it is analyzed optically.
However, although the theoretical foundations of this detection method are well-established at this time, there is no equipment for implementing this method that is capable of precisely determining the appearance and/or levels of solid matter in petroleum fluids with extreme densities (heavy oils).
In fact, for the specific fluids, the density is such that, even with small sample volumes and high light powers, the precision of the measurements is quite insufficient.